Process for the optical scanning of an object and device for the implementation of said process

ABSTRACT

A device for optically scanning an object includes a nozzle which is connected to a source of pressurized liquid. The nozzle generates a liquid stream which can be directed at the object. The device further includes a laser which is arranged to direct a beam of light at the object in order to scan the latter, and a sensor for receiving and analyzing light reflected from the object. The laser and the nozzle are positioned relative to one another in such a manner that light reflected from the object enters the liquid stream which then conducts the reflected light to the nozzle. The nozzle is connected to the sensor by at least one optical fiber which functions to conduct the reflected light from the nozzle to the sensor. One or more additional optical fibers may be provided to conduct light from the laser to the nozzle. The liquid stream then serves not only to conduct reflected light from the object to the nozzle but also to conduct the light used for scanning from the nozzle to the object.

TECHNICAL FIELD

The invention relates to a process, according to the preamble of claim1, for the optical scanning of an object as well as a device forcarrying out the process.

PRIOR ART

It is known to use linear and mechanical light deflectors which causeangular deflection for the optical detection or measurement of objectsand their surfaces. Relative motion of the light and the surface to bescanned is required if an action or a change is to be observed in thex-y plane. In contact activated or quasi-contact activated objectscanning a light conductor can simultaneously serve for lighttransmission to the object and receiving transmissions to the sensor, aswell as for image point definition. Particularly in conjunction withflexible optic fibers, the range of application of tuned detectionsystems is expanded to include a scanning principle having manyvariations, e.g., in the detection of bar codes or when OCR readinginstruments are employed.

In many applications, however contact with an object or quasi-contact bya solid light conductor is not possible. In critical environments, e.g.,in the presence of high temperatures or humidity, or aggressive mediasuch as dust, smoke, vapor, interfering light or radioactivity, orinterfering surface coatings due to liquid, dust, foam or othersubstances, it is not possible to use solid light conductors. Similarly,the use of solid light conductors is excluded in the optical scanning ofobjects having a critical consistency or geometry such as powdered orparticulate products, products with a fibrous surface structure,secreting organic substances or fluids enriched with suspendedsubstances.

An optical probe for applying a light cable to an object is known fromthe West German Offenlegungsschrift 15 98 004 and consists of atransparent, balloon-like and flexible membrane filled with a lightconducting liquid which can be replenished via a reservoir and a supplyline in order to maintain a specified static pressure in the balloon. Abundle of optical fibers whose ends are disposed in the liquid beforethe membrane opens into, and forms a seal with, the balloon. Light canbe thrown onto an object via the optical fibers, the liquid and themembrane and then reflected and conducted back to a receiving stationthrough the membrane, the liquid and the optical fibers. With such adevice, however, it is not possible to perform an optical scan in theabove-mentioned critical environment.

TECHNICAL OBJECT

It is accordingly an object of the invention to provide a process and adevice for the optical scanning of an object which cannot be subjectedto a contactless scan, or to a contact-activated scan, using a solidlight conductor, because the object is in a critical environment, or isprovided with interfering surface coatings, or has a consistency orgeometry which does not permit contactless or contact-activated scanningby means of a solid light conductor.

DESCRIPTION OF THE INVENTION

According to the invention, the solution to this object is in thefeatures of the process of claim 1; devices for carrying out the processare characterized in claims 3 and 13. Additional advantageousembodiments of the invention are contained in the remaining subclaims.

The invention has the great advantage that by means of the same, opticalobject scanning is possible even for those applications wherecontactless scanning with light only, or contact-activated scanningusing a solid light conductor, was not possible until now. Thus, the"gist" of the invention is that the combination of a solid lightconductor and a liquid light conductor in the form of a liquid streamserves as a light conductor. The transmitted light beam or light ray isincorporated in the liquid stream in a coupling station and is nowdirected onto the surface of the object to be scanned together with theliquid stream. After impingement of the liquid stream upon theimpingement point, the transmitted light is at least partiallyreflected, conducted back within the liquid stream counter to the flowdirection and separated from the liquid stream. The index of refractionof the liquid is advantageously taken into account in the couplingstation, e.g., by appropriate selection and design of an optical systemas a coupling station. This mode of object scanning is accordinglycontact-activated object scanning in which the scanning light conductoris a more or less fine liquid stream whose liquid is regenerated or canbe disposed of.

By using the liquid stream as a light conductor, the contact-activatedobject scanning can occur in a critical environment, e.g., at hightemperatures and humidity levels, in aggressive media such as dust,smoke, vapor or interfering light, or even in the presence ofradioactivity. The invention is intended especially for the opticalscanning of objects having interfering surface coatings which can beremoved for a period of time or continuously by means of a liquidstream, e.g., liquid, dust or foam present on the surface of the objectare washed away therefrom by the impingement pressure of the liquidstream. Similarly, the scanning of objects having a critical consistencyor geometry is possible using the invention, e.g., the scanning ofpowdered or particulate material, bulk materials, objects having afibrous surface structure, secreting organic substances or liquidscontaining suspended substances.

Advantageously, the liquid stream determines the size and position ofthe scanning point on the object. It is necessary to ensure that theliquid used is light conductive for the wavelength of the lightemployed. The liquid light conductor can accordingly serve both as alight conductor to the object and as a return conductor for thereflected light to signal processing.

In principle, it is possible to direct the transmitted light, outside ofthe liquid stream, onto the impingement point of the latter on theobject and to incorporate reflected light in the liquid stream at theimpingement point for return conduction.

BRIEF DESCRIPTION OF THE DRAWING

Examples of the invention are displayed in the drawing and describedbelow with the following illustrations showing:

FIG. 1 a schematic illustration of a device for carrying out the processof the invention and having solid light conductors, e.g., flexibleoptical fibers, between the scanning head and the light source,

FIG. 2a a diagrammatic layout of the device consisting of a scanninghead, conveying system, light source and sensor with the last two beingconnected to the scanning head by a solid light conductor,

FIG. 2b an embodiment of the device of FIG. 2a in which the solid lightconductor serves for back-and-forth conduction of the light from thescanning head,

FIG. 2c a device according to FIG. 2a in which the light source and thesensor are inside the scanning head,

FIG. 3 a device with two scanning heads each of which generates a liquidstream, one serving for outward conduction of the transmitted light beamand the other for return conduction of the reflected light beam, thesupply of the scanning heads corresponding to that in FIG. 2a,

FIG. 4 a device for the production of a liquid stream, the transmittedlight being directed onto the impingement point from outside of theliquid stream and reflected light being conducted back within the liquidstream,

FIG. 5 a device with a manifold scanning head for the production of aplurality of liquid streams each of which has a light source, a sensorpanel and a supply line from a common conveying system associatedtherewith,

FIG. 6 a technical exemplary embodiment of a device according to FIG. 1,

FIG. 7 a plan view of the end face of the common fiber bundle for thetransmitting and receiving fibers in the scanning head of FIG. 6,

FIG. 8 the design of a scanning head as a tube for inspecting theinteriors of objects,

FIG. 9 the design of a scanning as a flexible hose for inspecting theinteriors of cavities such as, for example, tubes and

FIG. 10 the deflection of the liquid stream with an electrical ormechanical deflecting instrument in order to produce relative motionbetween the scanning point and the object by controlled movement of theliquid stream over the object.

MODES OF EXECUTING THE INVENTION

FIG. 1 shows a diagrammatic layout of a device for the optical scanningof an object by means of a liquid stream produced from light-conductingliquid. The liquid stream is hereafter referred to as the scanningstream. A light source 1, which can be a laser light source, generates alight beam which is focused and delivered to a solid light conductor byan optical system. The term "optical system" will be understoodgenerally to include an appropriately arranged and designed module whichis capable of generating an optical effect such as projection,enlargement, focusing and the like. "Light conductor" will beunderstood, in particular, to encompass solid optical fibers which canbe either transmitting fibers or receiving fibers. "Nozzle" will beunderstood to mean an appliance which can generate a liquid streammechanically as well as electrically or magnetically.

The transmitting fiber 3 is guided, in a flexible cable 4, to a scanninghead 5 consisting, for example, of a cylindrical housing 6 whichsurrounds a cavity 7. The lower end of the housing 6 has a fine opening8 which constitutes a nozzle, for instance. An optical system 9 isdisposed in the cavity 7 of the scanning head 5 in the upper regionthereof. Similarly, at least one receiving fiber 10 is guided within thecable 4 and, like the transmitting fiber 3, ends inside the scanninghead 5 and above the optical system 9. The other end of the receivingfiber 3 is disposed opposite an optical system 11 and the latter issituated opposite an opto-electrical sensor 12 which can, for example,be a diode.

A liquid which is preferably light-conducting for the wavelength of thelight being employed is located in a container 13. A conveying system 14for the liquid is connected with the scanning head 5 by a liquid supplyline 15 which opens into the cavity 7 of the housing 6 The liquid can beconveyed into the cavity 7 of the scanning head 5 via the conveyingsystem 14. The conveying system can, in general, include a conveyingpump or dosing pump, valves, pressure regulating means and filters. Thescanning head can be supplied with the light-conducting liquid from anet or a tank or from the liquid environment surrounding the object. Ascanning stream 17 is formed from the liquid by means of the conveyingsystem 14 and the nozzle 8 and is directed onto an object 18 where itimpinges the surface 21 of the object at an impingement point 16. Asystem supply unit 22 functions to supply the light source 1 as well asthe sensor 12 and conveying system 14. The signals originating in thesensor 12 are processed in a signal processing instrument 23 andcompared with a reference signal, for example.

The operation of the device is as follows:

Light-conducting liquid is conducted from the container 13 into thecavity 7 of the scanning head 5 by the conveying system 14 and is therepressed outwards through the nozzle 8 in the form of the fine scanningstream 17 by generating a pressure. This scanning stream is maintainedthroughout the entire scanning period. At the same time, a light beam isgenerated by the light source 1 and, after focusing on the transmittingfiber 3, is introduced into the volume of liquid within the cavity 7 viathe optical system 9. The transmitted light is so focused by the opticalsystem 9 that it is conducted directly outwards through the nozzle 8together with the scanning stream 17. The scanning stream 17 serves asan additional, liquid light conductor. The light is reflected at theliquid/air boundary within the scanning stream 17 in accordance with thelaws of optics and is conducted downwards within the scanning stream 17to the impingement point 16 on the object 18.

At the impingement point 16, the transmitted light is at least partiallyreflected and conducted back within the scanning stream 17 so that, inthis case, the scanning stream 17 simultaneously serves for outgoing andreturn conduction of the light. The reflected light is separated fromthe liquid by means of the optical system 9 and delivered to thereceiving fiber 10 and thereafter falls, via the optical system 11, ontothe sensor 12 whose electrical output signals are processed in thesignal processing instrument 23. Upon movement of the object 18 in thedirection of the motion arrow 82, which is to the left in FIG. 1, thesurface 21 of the object 18 is scanned at the impingement point 16 inaccordance with the movement.

Diagrammatic layouts of the device, which are designed similarly to thedevice of FIG. 1, are shown in FIGS. 2 to 5. FIG. 2a illustrates ascanning head 35 to which liquid 29 is conveyed by a liquid supply line32. In the scanning head 25, the liquid is converted into a scanningstream 33 which is directed onto an object 24. A light source 27 isconnected with the scanning head by a light conductor 30 and a sensor 28is connected with the scanning head by a light conductor 31.

FIG. 2b shows a layout in which a light conductor 34 serves for bothoutgoing and return conduction of the light with the reflected lightbeing deflected by a deflecting instrument 35 and delivered to thesensor 28. FIG. 2c shows another diagrammatic layout possibility inwhich the light source and the sensor 28 are located inside a scanninghead 26. As in FIGS. 2a and 2b, the scanning head 26 is supplied withthe scanning liquid 29 from a conveying system via a liquid supply line32.

FIG. 3 illustrates a device having two scanning heads 36 and 36' whichare arranged next to one another and are supplied with the scanningliquid 29 by means of respective liquid supply lines 39, 39'. Eachscanning head 36, 36' generates a scanning stream 37, 38 and bothscanning streams are directed towards a common impingement point on theobject 24. The light is incorporated in the scanning stream 37 whilereflected light, on the other hand, is incorporated in the secondscanning stream 38 and conducted back.

FIG. 4 shows a device in which only the liquid supply line 32 and thereceiving light conductor 31 are led into the scanning head 40. A lightbeam 41 is pointed directly at the impingement point of the scanningstream 33 on the object 24 from outside the scanning stream and it isonly the reflected light which is incorporated in the scanning stream 33at the impingement point and conducted to the sensor 28 via the scanninghead 40.

FIG. 5 illustrates a device having a manifold scanning head 42 whichgenerates a plurality of scanning streams 33. Light issuing from thelight source 27 can be incorporated in each scanning stream and returnof the reflected light takes place as in FIG. 1 or 2. All of the returnreceiving conductors lead to a sensor panel 43 for appropriate furtherprocessing. The liquid supply line 32 for supplying the scanning liquid29 from a conveying system functions to produce the plurality ofscanning streams simultaneously.

FIG. 6 shows a technical layout of the device according to theinvention. A plate 46 is suitably arranged inside a detector housing 44and a holder 49 is suitably mounted in or on the plate. On the one sideof the plate 46, the holder 49 carries a diode laser within a couplingoptical system 45. At least one transmitting fiber 47 leads into theholder 49 on the opposite side and is secured there. Similarly, anotherholder 29' is arranged in or on the plate 46 and an opto-electricalsensor 52 is disposed at one side of this holder 29'. At least onereceiving fiber 48 enters the opposite side of the holder and an opticalsystem 51 can be located between the end of the receiving fiber 48 andthe sensor 52. The transmitting and receiving fibers 47, 48 are guidedto a scanning head 55 inside a flexible cable 54 as is a liquid supplyline 53.

The scanning head consists of an elongated housing 56 which ispreferably cylindrical and has a core 58 therein. The core 58 has acavity 59, e.g., a bore, into which the liquid supply line 53 opens. Anoptical system 57 is located at the upper end of the cavity 59 and theend faces of the transmitting and receiving light conductors 47, 48 areadjacent to the optical system 57; the ends of the light conductors 47,48 are suitably held in the core 58 for this purpose. The lower end ofthe cavity 59 is closed by a nozzle 60. Upon introduction of thescanning liquid into the cavity 59 under pressure, a fine scanningstream 61 is formed from the scanning liquid by the nozzle 60 andimpinges on an object 62 at the scanning point 63. If light from thediode laser 45 is simultaneously conducted through the transmittingfiber 47, then the optical system 57 incorporates the transmitted lightin the scanning stream 61. Return conduction of the reflected light andevaluation of the same occurs as described for FIG. 1.

FIG. 7 is a plan view of the end face 65 of the fiber bundle which isformed from the transmitting and receiving fibers 47,48 and is locatedabove the optical system 57 of FIG. 6. The single light conductor 47here serves as a transmitting fiber and is surrounded by a plurality ofreceiving fibers 48 arranged in a circle.

FIGS. 8 to 10 illustrate examples of the device which are adjusted tovarious products. In FIG. 8, the scanning head consists of a scanningtube 69 which is closed at its lower end. A peripheral nozzle 70 fordischarge of a scanning stream 71 is arranged at the circumference ofthe scanning tube. The scanning tube 69 extends into a body 66 having acavity 67 with an inner wall to be scanned. If the scanning tube 69 isturned during the scanning procedure while being slowly pushed into thecavity 67, the entire inner wall can be imaged, e.g., spirally.

FIG. 9 shows the design of the scanning head as a flexible scanning hose73 provided, at its front end, with two spaced guide members 74,74'serving to guide the scanning hose 73 in an elongated hollow body 72which can be a curved tube. The lower end of the scanning hose 73 isclosed and its circumferential wall has a peripheral nozzle 75 for theproduction of a scanning stream 76 between the two guide members 74,74'.Upon insertion of the scanning hose 73 in the hollow body 72, the innerwall of the latter can be scanned along the line traveled by thescanning stream 76.

FIG. 10 illustrates a scanning head 77 the lower end of which extendsinto a chamber 78 containing a deflecting instrument 79. This deflectinginstrument 79 serves to deflect the scanning stream 80 which isaccordingly directed onto an object 81 at an angle of deflection beta asreferred to the direction of discharge of the scanning stream 80 fromthe scanning head 77. The scanning stream 80 passes through thedeflecting instrument 79 which can operate electrically or mechanically.If the deflecting instrument 79 operates electrically, then the scanningliquid employed must not only be light-conducting but also capable ofbeing electrically deflected. In this manner, the scanning stream 80 canbe guided over the object 81 in a predetermined fashion by control ofthe deflecting instrument 79 so that no relative movement between theobject itself and the scanning head is required here to collectinformation.

Industrial Utility

The invention is intended for the optical scanning of objects havinginterfering surface coatings which can be removed for a period of timeor continuously by a liquid stream. Similarly, the scanning of objectshaving a critical consistency or geometry is possible using theinvention, e.g., the scanning of powdered or particulate material, bulkmaterials, objects having a fibrous surface structure, secreting organicsubstances or liquids with suspended substances.

The invention is likewise suited for the local inspection of radioactivecomponents which are located in a wet environment within a protectedradiation area. This allows the local surface condition and thetemperature to be determined. The invention can also be used in the wettreatment of reprographic materials which are located in an environmentsuch as wetness, brine or foam, or in an enclosed processing line. Here,densitometric values are obtained as identification criteria.

Moreover, the invention can be used during the chemical treatment oftextile materials in a processing line where the environment can consistof wetness, vapor, brine or foam bubbles. The identification criteriadetected are stretching of the material over the width of the path oftravel at different locations of the treatment zone, color, otherdefects, color defects or weaving defects.

In particular, the invention can be used with advantage wherever acooling emulsion which has been enriched with finely divided materialresidues such as metal residues covers the immediate processing locationof the object as is the case in many areas of technology where objectsundergo material-removing operations. Cracks, chipped areas or otherdefects due to material processing can here be observed and detecteddirectly at the location of engagement of the material-removing toolsince the cooling emulsion is pushed away by the liquid stream and theprocessing point is thereby exposed.

Furthermore, the invention can advantageously be used during dressing ofthe warp threads in a processing line when the layer of threads ispressed by a calender. The environment can here be vapor, wetness ordissolved substances and the identification criterion a torn individualthread which is coiled around the calender.

LIST OF REFERENCE NUMERALS

1 Light Source

2 Optical System

3 Light Conductor (Transmitting Fiber)

4 Flexible Cable

5 Scanning Head

6 Housing

7 Cavity

8 Nozzle

9 Optical System

10 Light Conductor (Receiving Fiber)

11 Optical System

12 Sensor

13 Container

14 Conveying System (Pump)

15 Liquid Supply Line

16 Impingement Point

17 Liquid Stream (Scanning Stream)

18 Object

19,20 Directional Arrows

21 Surface of the Object

22 System Supply Unit

23 Signal Processing Instrument

24 Object

25,26 Scanning Heads

27 Light Source

28 Sensor

29 Scanning Liquid

30 Transmitted Light Conductor

31 Receiving Light Conductor

32 Liquid Supply Line

33 Scanning Stream

34 Common Light Conductor in both Directions

35 Deflecting instrument

36,36' Scanning Heads

37,38 Scanning Streams

39,39' Liquid Supply Lines

40 Scanning Head

41 Light Ray

42 Scanning Head

43 Sensor Panel

44 Detector Housing

45 Diode Laser

46 Plate

47 Transmitting Fibers

48 Receiving Fiber

49,49' Holder

50,50' End of the Fibers

51 Optical System

52 Sensor

53 Liquid Supply Line

54 Flexible Cable

55 Scanning Head

56 Housing

57 Optical System

58 Core

59 Bore

60 Nozzle

61 Liquid Stream

62 Object

63 Scanning Point

64 Tee

65 End Face of the Bundle of Transmitting and Receiving Fibers

66 Body

67 Cavity

68 Opening

69 Scanning Tube

70 Nozzle

71 Liquid Stream

72 Elongated Hollow Body

73 Flexible Scanning Hose

74,74' Guide Members

75 Nozzle

76 Liquid Stream

77 Scanning Hose

78 Chamber

79 Deflecting Instrument

80 Liquid Stream

81 Object

I claim:
 1. Process for the optical scanning of an object using a finelight beam which is moved relative to the object and is conducted into alight-conducting liquid, and an opto-electrical sensing and analyzinginstrument for analyzing the reflected light, characterized in that theliquid is subject to a hydrodynamic pressure or an acceleration and aliquid stream (17,33,37,38,61,71, 76,80), which is directed onto theobject (18,24,62, 66,72,81) to be scanned and rinses the same at thescanning location (16,63), is generated, the light being incorporated inthe liquid stream and being directed within the same onto theimpingement point (16,63) of the liquid stream upon the object, and thereflected light thereafter being conducted back within the liquidstream, separated from the same and delivered to the sensing andanalyzing instrument (12,22;28;43;52).
 2. Device for carrying out theprocess according to claim 1 characterized by the combination of a solidlight conductor, a liquid light conductor in the form of a liquid streamwhich is directed onto the object at the scanning point, and aninstrument for incorporating the transmitted light in the liquid streamand for separating the reflected light from the liquid stream.
 3. Devicefor the optical scanning of an object using a fine light beam which ismovable relative to the object and can be conducted into alight-conducting liquid, and an opto-electrical sensing and analyzinginstrument for analyzing the reflected light, characterized by(a) ascanning head (5,25,26,36,36',40,42,55, 69,73,77) which has a nozzle(8,60,70,75) and is near the object (18,24,62,66,72,81) (b) a conveyingsystem (14) which conveys the light-conducting liquid to the scanninghead (5,25,26, 36,36',40,42,55,69,73,77) from a container (13) (c) theliquid being subjected to a pressure or an acceleration, being formedinto a liquid stream (17,33,37,38,61,71,76,80) by the nozzle(8,60,70,75) and directed onto the object (18,24,62,66,72,81) (d) aninstrument (9,57) within the scanning head for incorporating thetransmitted light in the liquid stream and/or separating the reflectedlight from the liquid stream in order to deliver the reflected light tothe sensing and analyzing instrument (12,33;28,43,52).
 4. Deviceaccording to claim 3, characterized in that the scanning head (5,55) hasa cavity (7,59) into which a supply line (15,53) from the conveyingsystem (14) opens, the instrument (9,57) for incorporating and/orseparating the light being disposed above the nozzle (8,60,70.75) andbeing an optical system.
 5. Device according to claim 4, characterizedin that the light source (27) for generating the transmitted lightand/or the sensing instrument (28) for receiving the reflected light islocated within the scanning head (26).
 6. Device according to claim 4,characterized in that the optical system (9,57) for incorporating and/orseparating is located directly above the nozzle (8,60) of the scanninghead (5,55) in the direction of the liquid stream (17,61) and in theupper portion of the cavity (7,59).
 7. Device according to claim 3,characterized in that the scanning head (36,36';42) is provided with aplurality of nozzles for generating a plurality of liquid streams(33,37,38) and each has a light source (27), an instrument forincorporating or separating the light and a sensing and analyzinginstrument (28,43) associated therewith.
 8. Device according to claim 3,characterized by at least one transmitting and/or receiving opticalfiber (3,30,34,47;10,31,34,48) which is arranged between the lightsource (1,27,45) and the scanning head (5,26,36,36',40,42,55,69,73,77)or between the sensing and analyzing instrument (11,23;28;43;52) and thescanning head (5,26,36,36',40,42,55,69,73,77), extends into the latterand terminates above the instrument (9,57) for incorporating and/orseparating.
 9. Device according to claim 3, characterized in that thescanning head consists of a tube (69,73) into which the liquid isconducted and which is closed at its lower end, the nozzle (70,75) beingperipherally disposed at the circumference of the tube.
 10. Deviceaccording to claim 3, characterized by an electrically or mechanicallyoperating deflecting instrument (79) for the liquid stream (80) which isarranged behind the scanning head (77) and through which the liquidstream (80) passes for controlled deflection thereof.
 11. Process forthe optical scanning of an object using a fine light beam which is movedrelative to the object and is conducted from the object in alight-conducting liquid, and an opto-electrical sensing and analyzinginstrument for analyzing the reflected light, characterized in that theliquid is subject to a hydrodynamic pressure or an acceleration and aliquid stream, which is directed onto the object to be scanned andrinses the same at the scanning location, is generated, the light beingdirected toward the impingement point of the liquid stream upon theobject from outside the liquid stream at an angle greater than zero, andthe reflected light thereafter being incorporated into the liquid streamat the impingement point and being conducted within the liquid stream,separated from the same and delivered to the sensing and analyzinginstrument.
 12. Device for the optical scanning of an object using afine light beam which is movable relative to the object and can beconducted into a light-conducting liquid, and an opto-electrical sensingand analyzing instrument for analyzing the reflected light,characterized by two scanning heads which have nozzles and are near theobject, a conveying system which conveys the light-conducting liquid tothe scanning heads from a container, the liquid being subjected to apressure or an acceleration, being formed into two liquid streams by thenozzles and the two streams being directed onto the same point of theobject, a first instrument within one scanning head for incorporatingthe transmitted light in the respective liquid stream for impingementupon and reflection at said point of the object, and a second instrumentwithin the other scanning head for separating the reflected light fromthe respective liquid stream in order to deliver the reflected light tothe sensing and analyzing instrument.